• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.396-400
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• 2003

A new synthesis process for nano laminating Ti$_3$SiC$_2$ has been developed using TiCx (x=0.67) and Si powder as starting materials by a reaction hot pressing. Bulk Ti$_3$SiC$_2$ was fabricated using a green body consisting of TiCx and Si by a hot pressing under the pressures of 25 MPa at 1420-1550 $^{\circ}C$ for 90 min. The synthesized Ti$_3$SiC$_2$ was consisting of only TiCx and Ti$_3$SiC$_2$. The relative density of sintered bulk Ti$_3$SiC$_2$ was increased as the hot pressing temperature was increased, which was mainly due to the increase in TiCx contents in synthesized Ti$_3$SiC$_2$. The synthesized Ti$_3$SiC$_2$ bulk was consisted of nano sized lamella structure of 20-100 nm in thickness. It was found that TiCx particles in Ti$_3$SiC$_2$ would increase the 3-point bending strength of synthesized Ti$_3$SiC$_2$ bulk. The maximum 3-P. bending strength of synthesized Ti$_3$SiC$_2$ bulk was more than 800 MPa. The Vickers hardness of synthesized Ti$_3$SiC$_2$bulk was as low as 5 Gpa, which was decreased with the indentation load. The quasi-plastic deformation behaviors were observed around indentation mark on Ti$_3$SiC$_2$.

• 대한기계학회논문집A
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• 제39권2호
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• pp.169-177
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• 2015

내접형 기어펌프에 사용되는 지로터의 경우, 소결 공정기술의 발달로 복잡한 형상의 가공이 용이하며 내구성과 소형화의 장점이 있으나, 자동차의 연비효율 개선을 위한 유량증대 및 소음저감을 위한 연구가 요구되고 있다. 본 논문에서는 기존의 병진이동에 의한 지로터 치형의 형상조합 알고리즘이 가지는 형상 불연속성을 개선하기 위하여 회전이동 및 병진이동을 이용한 형상조합 알고리즘을 개발하였으며, 이를 토대로 개발된 설계 프로그램을 이용하여 3-타원이 조합된 경우와 타원 1-인벌루트-타원 2 이조합된 경우에 대해 치형형상을 도출하고, 형상에 따른 로터의 주요성능(유량, 유량맥동, 미끄럼률 및 압력각)을 계산하였다. 해석결과를 토대로 조합된 치형형상에 대한 최적설계를 수행하였으며, 기존 치형과의 성능 비교를 통하여 설계의 타당성을 검증하였다.

• Progress in Superconductivity
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• 제11권2호
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• pp.87-91
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• 2010

We fabricated the polyacrylic acid (PAA)-doped $MgB_2$ bulks and characterized their lattice parameters, actual C substitutions, microstructures, and critical properties. The boron (B) powder was mixed with PAA using N,N-dimethylformamide as solvent and then the solution was dried out at $200^{\circ}C$ and crushed. The C treated B powder and magnesium powder were mixed and compacted by uniaxial pressing at 500 MPa, followed by sintering at $900^{\circ}C$ for 1 h in high purity Ar atmosphere. We observed that the PAA doping increased the MgO amount but decreased the grain size, a-axis lattice constant, and critical temperature ($T_c$), which is indicative of the C substitution for B sites in $MgB_2$. In addition, the critical current density ($J_c$) at high magnetic field was significantly improved with increasing PAA addition: at 5 K and 6.6 T, the $J_c$ of 7 wt% PAA-doped sample was $6.39\;{\times}\;10^3\;A/cm^2$ which was approximately 6-fold higher than that of the pure sample ($1.04\;{\times}\;10^3\;A/cm^2$). This improvement was probably due to the C substitution and the refinement of grain size by PAA doping, suggesting that PAA is an effective dopant in improving $J_c$(B) performance of $MgB_2$.

• 한국결정성장학회지
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• 제17권5호
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• pp.210-216
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• 2007

극청정 가스필터용 다공성 멤브레인을 제조하기 위해 금속산화물 분말의 in-situ한 환원/소결 공정을 이용하였다. 또한 기공도의 향상을 위해 solid pore forming agent로써 구형의 폴리머 입자를 첨가하여 금속 섬유를 사용한 멤브레인과 비슷한 52%의 기공도를 가지는 니켈 멤브레인을 제조하였다. 제조된 니켈 멤브레인은 폴리머의 첨가에 따라 평균기공크기와 기공도가 증가하였다. 한편 환원/소결 온도가 $800^{\circ}C$에서 $1000^{\circ}C$로 상승함에 따라 평균기공크기와 기공도는 감소하였다. 이는 환원/소결 온도가 상승함에 따라 격자확산 및 입계확산이 진행되어 멤브레인의 수축률 증가를 일으켰기 때문이다.

• 한국세라믹학회지
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• 제34권1호
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• pp.70-78
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• 1997

3Y TZP/SUS316계 경사기능재료를 슬립캐스팅법을 이용하여 제조하였다. 슬립캐스팅 공정에서 석고몰드를 대체하기 위해 알루미나몰드를 제조하였고, 3Y-TZP/SUS316 2상 슬러리의 최적 분산조건을 ESA, 점도계, 침전거동의 관찰 등을 통해 결정하였으며, 석고몰드와 알루미나몰드로 캐스팅한 시험편의 제반 특성을 소결수축율변화, 건조 및 소결거동, 미세구조 관찰 등으로 조사하였다. 그 결과 알루미나몰드를 사용하여 제조된 시험편에서는 석고몰드 사용시 나타나는 표면에서의 오염이 관찰되지 않았으며, 각 층의 두께조절이 쉬웠고 높은 재현성을 나타냄을 알 수 있었다. 특히 알루미나몰드를 사용하여 제조한 SUS316에서는 어떤 열화현상도 관찰되지 않았다. 결국 슬립캐스팅 공정으로 3Y-TZP/SUS316계 경사기능재료를 제조함에 있어서 기존의 석고몰드보다 다공질 알루미나몰드의 사용이 바람직하다는 것을 알 수 있었다.

• 한국세라믹학회지
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• 제34권1호
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• pp.23-30
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• 1997

SrCO3 TiO2, 그리고 Nb2O5를 출발원료로 하여 환원분위기하에서 반도성 SrTiO3 소결첼르 제조하였다. 반도성 다결정 소결체 내에서 acceptor 역할을 할 수 있는 Na과 K 이온을 입계를 따라 80$0^{\circ}C$~120$0^{\circ}C$ 온도범위에서 확산시킨 후, 열처리조건에 따른 입계의 전기적 화학적 특성을 고찰하였다. 이차열처리한 소결체의 입계에는 일정한 전기적 포텐셜장벽과 이에 상관된 전자고갈영역이 형성되어 비선형적인 전류-전압 특성을 보이고 문턱전압(threshold voltage)은 10~70V, 입계포텐셜장벽은 0.1~2eV의 크기를 나타내었다. Na과 K 이온은 입계로부터 입자내부로 확산하여 20~50 nm 깊이의 확산층을 형성하며, 이들 확산층에서 Na 또는 K과의 치환에 기인하여 Sr농도가 감소하였으며 치환에 따른 전기적 중성유지를 위하여 산소 vacancy 농도가 증가하였다.

• 한국전기전자재료학회논문지
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• 제29권10호
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• pp.665-670
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• 2016

Prevailing dissemination of machine tools and cutting technology have caused drastic developments of high speed dry machining with work materials of high hardness, and demands on the high-hardness-materials with high efficiency have become increasingly important in terms of productivity, cost reduction, as well as environment-friendly issue. Addition of Si to TiAlN has been known to form nano-composite coating with higher hardness of over 30 GPa and oxidation temperature over $1,000^{\circ}C$. However, it is not easy to add Si to TiAlN by using conventional PVD technologies. Therefore, Ti-Al-Si-N have been prepared by hybrid process of PVD with multiple target sources or PVD combined with PECVD of Si source gas. In this study, a single composite target of Ti-Al-Si was prepared by powder metallurgy of MA (mechanical alloying) and SPS (spark plasma sintering). Properties of he resulting alloying targets were examined. They revealed a microstructure with micro-sized grain of about $1{\sim}5{\mu}m$, and all the elements were distributed homogeneously in the alloying target. Hardness of the Ti-Al-Si-N target was about 1,127 Hv. Thin films of Ti-Al-Si-N were prepared by unbalanced magnetron sputtering method by using the home-made Ti-Al-Si alloying target. Composition of the resulting thin film of Ti-Al-Si-N was almost the same with that of the target. The thin film of Ti-Al-Si-N showed a hardness of 35 GPa and friction coefficient of 0.66.

• 한국전기전자재료학회논문지
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• 제29권10호
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• pp.601-607
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• 2016

Piezoelectric thick films of soft $Pb(Zr,Ti)O_3$ (PZT) based commercial material (S55) were fabricated using a conventional tape casting method. Ag-Pd electrodes were printed on the piezoelectric film at room temperature and all 5 layered films with a dimension of $12mm{\times}16mm$ were successfully laminated for a multi-layered piezoelectric ceramic actuator. The laminated specimens were co-fired at $1,100^{\circ}C$ for 1 h. A flat layered and dense microstructure was obtained for the $112{\mu}m$ thick piezoelectric actuator after sintering process. Thereafter, a prototype piezoelectric speaker was fabricated using the multi-layered piezoelectric ceramic actuator which can operate as a bimorph. Its SPL (sound pressure level) characteristic was also evaluated for speaker application. Frequency response revealed that the output SPL with a root mean square voltage of 10 V increased gradually to the highest peak of 87.5 dB for 1.5 kHz and exhibited a relatively stable behavior over the measured frequency range (${\leq}20kHz$) at a distance of 10 cm, implying that the fabricated piezoelectric speaker is potential for speaker applications.

• Advances in materials Research
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• 제2권3호
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• pp.133-140
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• 2013

This paper aims to focus on the microwave processing of thick films which is a fast, cheap technique and could be the alternative to the currently used conventional high temperature processing technique. Microwave processing has gained worldwide acceptance as a novel method for heating and sintering a variety of materials, as it offers specific advantages in terms of speed, energy efficiency, process simplicity, finer microstructures and lower environmental hazards. Silver conducting thick films were prepared and processed in the household microwave oven. The films sintered at different time period by keeping the other parameter such as microwave power, film thickness etc constant. The microstructure analysis revealed that the surface morphology of the microwave processed films become compact with respect to the processing time. The sheet resistance for microwave sintered silver films is in the range of 0.003 to $1.207{\Omega}/{\Box}$ where as the films fired at 750 and $850^{\circ}C$ showed the resistance of 0.009 and $0.003{\Omega}/{\Box}$ which can be comparable. The results revealed that the microstructure of the microwave sintered films has more uniform and compact surface than that of the conventionally fired films. The paper reports upon the preparation of silver thick film by screen printing technique and processing the same by microwave which also compared with the conventionally processed thick films.

• Journal of Advanced Marine Engineering and Technology
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• 제38권5호
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• pp.589-601
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• 2014

Natural gas hydrate (NGH) is emerging as a new eco-friendly source of energy to replace fossil fuels in the 21st century. It is well known that the Natural Gas Hydrate contains large amount of natural gas about 170 times as much as its volume and it is easy to be stored and transported safely at about $-20^{\circ}C$ under atmospheric pressure due to so called "self-preservation effect". The option of gas transport by gas hydrate pellets carrier has been investigated and developed in various industry and academy. The natural gas hydrate pellet carrier is on major link in a potential gas hydrate process chain, starting with the extraction of natural gas from the reservoir, followed by the production of hydrate pellets and the transportation to an onshore terminal for further processing or marketing. In recent years, Korean project team supported by Korean Government has been working on the development of NGH total systems including novel NGH carrier since 2011. In order to increase the knowledge on the NGH pellet carrier developed and to understand the major hazards that could have significant impact on the safety of the vessel, this paper presents and evaluates the pros and cons of cargo holds, loading and unloading systems through the analysis of current patent technology. Based on the proven and well-known technologies as well as potential measures to mitigate sintering and minimize mechanical stress on the hydrate pellet in the self-preservation state, this study presents the conceptual and basic design for NGH carrier.